Differential Equations

Intuitive

Explanations in this section should contain no formulas, but instead colloquial things like you would hear them during a coffee break or at a cocktail party.

Concrete

Linear Differential Operators by Lanczos - as all his books, useful and full of unusual ways to look at the subject.
TEN LESSONS I WISH I HAD LEARNED BEFORE I STARTED TEACHING DIFFERENTIAL EQUATIONS GIAN-CARLO ROTA

Abstract

The motto in this section is: the higher the level of abstraction, the better.

Why is it interesting?

Many of the most important equations in physics are differential equations.